I found listings that the Bushnell 28/2.8 is a M42 lens. Mean the mounting type is thread and the diameter is 42mm. Pentax makes an adapter... K to M42, others are available as well, but the quality varies. If you are not familiar with K mount features, then keep in mind that unlike a K mount lens, the screwmount will not allow for automatic-aperture-open. So if you adjust the aperture, the image will get dimmer unless you switch from MANUAL and AUTO modes on the lens.